The invention relates to a photometry controller for a camera having an electronic flash controlling capability and capable of photometry based upon reflection of an image from a film surface, and more particularly, to a photometry controller for controlling a circuit within a camera having TTL (through-the-lens) automatic electronic flash controlling capability and capable of photometry based upon reflection of an image from a film surface, which circuit is used to integrate a photocurrent produced by a photoelectric transducer element.
The photometry employed with cameras can generally be categorized, according to the distributed sensitivity to light incidence, into average photometry, a centrally biased photometry (or average photometry with emphasis on the central region) and spotwise photometry. These techniques of photometry are advantageous in one aspect and disadvantageous in another. In particular, when taking a picture of a person in a rear lighting condition, against the background of the sea or snow covered mountain or the like, the main subject to be taken such as a person will be subject to an underexposure if the average or centrally biased photometry is utilized. If the spotwise photometry is utilized when taking such a picture, a substantially proper exposure will be achieved, but peripheral objects which define the background will be subject to excessive overexposure. In either instance, the picture as a whole will be a poorly balanced photograph. To accommodate for this, there has been proposed a technique (Japanese laid-open patent application No. 36,229/1978) in which photometric values according to the spotwise photometry and the centrally biased photometry are obtained, and whenever the difference therebetween exceeds a given value, a median value of them is derived to provide an exposure control. However, when a great difference prevails in the brightness level as when the main subject is under a very dark illumination as compared with the background, it is desirable to reduce the difference in the exposure given to the main subject and to the background in a positive manner by performing a so-called daylight synchronized photographing operation in which light from an electronic flash is directed toward the main object.
TTL automatic electronic flash may cooperate with a camera capable of photometry of reflection from a film surface to provide a so-called TTL centrally controlled electronic flash system. The system is designed to activate the electronic flash at the time when shutter blades are fully open, in order to compensate for any lack of exposure given by natural light. Accordingly, until the shutter blades become fully open, a photometric circuit of the system operates to integrate a photocurrent which results from the incidence of natural light, and to integrate a photocurrent which results from the flashlight from the electronic flash after the shutter blades are fully open. Accordingly, when taking a picture of an object which is in the rear light, while utilizing the TTL automatic electronic flash, the incidence of natural light of a high intensity which prevails in the background region may, after its photometry, prevent the electronic flash from being activated until the shutter blades are closed again or if the electronic flash is allowed to emit flashlight, the resulting time interval for integration of the flashlight from the electronic flash is greatly reduced as compared with the time interval over which natural light is integrated. Hence, this arrangement fails to provide a sufficient flashlight from the electronic flash for a subject which is in the rear light, to reduce a difference in the exposure given to the subject and to the background to trim the general tone of the picture field.
To cope with this problem, the present applicant has previously proposed a photometry control apparatus (see Japanese laid-open patent application No. 140,825/1980) in which the time when an integration is initiated in the photometric circuit is delayed until immediately before the time when the synchro contacts are closed to allow the emission of flashlight from an electronic flash, thus allowing the ratio of the integration of the flashlight from the electronic flash to the integration of natural light to be increased.
With the described apparatus, it is necessary to selectively operate a photographing operation in which the relative ratio of integration of the flashlight from the electronic flash is increased as contrasted to a normal photographing operation, in accordance with a visual determination of a difference in the brightness level between the subject and the background by the user. However, a visual determination of differential brightness each time a picture is to be taken when utilizing an electronic flash is troublesome. In addition, an accurate determination of the difference in the brightness requires a degree of skill, presenting a great difficulty.